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We receive nickel plated parts that are pitted in only specific areas.

We currently have a 2" brass part plated by our sub-contractor with electroless nickel to .0003 max thickness mid level phosphorus over a base plating of copper. In the center of the part is a 1/4" diameter bore 1/2" deep with a smaller thru hole in the center.We are seeing pitting only inside the bottom of the 1/4 diameter bore and no where else. The pits are more frequent and larger in the corner of the bore bottom and where the smaller thru hole intersects the 1/4" bore. The pits are nickel plated so the pitting must be taking place before this process.We know the parts are pitt free before plating. What could cause this and how can it be eliminated?

Edward Dansbereger
Machine shop that sub-contracts - Stevensville, Maryland, USA
January 11, 2008

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Pitting could occur during plating. The electroless nickel reaction liberates hydrogen gas; the gas could form bubbles which stick to the surface. These pits typically are hemispherical in shape, and the problem may be solved by modifying solution agitation, part racking, or solution formulation modification. I'd have a talk with the plater.

James Totter, CEF
- Tallahassee, Florida
January 12, 2008